This invention relates to subarray antenna systems and in particular to subarray pattern control and null steering improvements in such systems.
A growing number of military radar systems require wideband scanning arrays with sidelobes below -40 dB, steered nulls, and other forms of active pattern control. Since the cost of a fully time delay steered array is prohibitive for many of these applications there is a need for subarraying feeds so that the time delay and/or null steering can be controlled at the relatively fewer subarray inputs, while the main aperture need only have conventional phase shifters.
A number of subarraying feeds of this type are described by R. Tang in the publication Survey of Time-Delay Beam Steering Techniques in Phased Array Antennas; Proceedings of The 1970 Phased Array Antenna Symposium, Artech House, Inc. Dedham, MA pp 254-260. Null steering circuits are described in detail in the publication of D. J. Chapman, entitled Adaptive Arrays and Sidelobe Cancellers; A Perspective, Microwave Journal, August 1977, pp 43-46. These publications together represent and are typical of the state-of-the-art in this area.
Subarray antenna systems utilizing such state-of-the-art circuits are subject to the undesirable effects of illumination truncation at the edge of the array. This results in high sidelobe pattern and limitations on the control of individual nulls and the ability to null entire regions of the subarray pattern.
Consequently, to date there is no known wideband technique for scanning a low sidelobe subarray. Present techniques require subarraying from very narrow band subarrays or from subarrays that are limited to -20 to -25 dB sidelobes. Accordingly, there currently exists the need for techniques and system functions that will provide the ability to scan over wide spatial angles with wide bandwidths and low sidelobes and that will permit improved control of nulling at both the array and subarray levels. The present invention is directed toward satisfying that need.